1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an inter-technology handoff method in an IP (Internet Protocol)-based mobile communication network including radio access networks that use different radio access protocols.
2. Description of the Related Art
Along with the rapid development of wireless communication technology, demands for IP-based wireless data service are growing. The technological development and user demands in the market have driven development and commercialization of wireless communication networks that differ in capacity, speed, and mobility support. FIG. 1 is a schematic view illustrating a cellular environment with different overlapped radio access networks. To provide communication services in the cellular environment, a mobile station (MS) must be equipped with multiple interfaces. Also, to provide communication services to the MS without interruption while it is roaming, an effective handoff technology is required.
Mobile IP service is available on existing IP networks. The mobile IP service is designed to reset a routing path for an MS that moves between networks in different subnets. By using the mobile IP service, the MS detects a new IP subnet (L3 movement detection), generates a new IP address or has it assigned, binds the IP address to the network, and transmits data to the IP address. The mobile IP operation is carried out when a physical connection (L2 connection) is completed between the MS and a new base station (BS), and the physical connection involves authentication and registration.
In other words, to implement a handoff between BSs or networks having different characteristics in terms of their respective service providers, QoS (Quality of Service), cell size, and mobility support, a physical connection to a new BS, an operation for authentication in regard to a handoff request from an MS and support of a continuous service between BSs, and an operation for resetting a routing path for seamless delivery of IP service must be carried out.
FIG. 2 is a flowchart illustrating a typical IP-based inter-technology handoff procedure. Referring to FIG. 2, an MS searches for BSs automatically autonomously or according to a network policy, detects a handoff situation, and decides to perform a handoff in step S201. A physical connection is established between the MS and a new BS in step S202 and messages are exchanged between old and new BSs, for authentication, QoS negotiations, location and mobility management in step S203. Then, an IP routing path is reset in step S204 according to Mobile IP practice.
Due to the complexity of an IP mobility operation, however, the mobile IP handoff procedure may cause a handoff delay, thereby degrading the quality of communication service.